Array modifier questions from a beginner
19:30 He basically duplicate the set of windows with CtrlD and then proceeded to deleting the array modifier that was copied during the duplicate fuction.

18:30 Ctrl L - It's basically a quick method to select a mesh and all it's joined elements. This is extremely useful if you have multiple sub-meshes joined together to form the main object. Sometimes you may want to select that one sub-mesh to apply a material or hide it temporarily.

Applying a modifier makes it permanent and irreversible. However you can undo it if it's still within the undo range. Usually you will want to apply modifier at the end of the modeling process.



Extra Note

Personally, I usually just hit L, this works in UV editor mode too when you want to select a UV island.